Electrical switches actuated by a swing arm having a roller at an end of the arm are well known in the art. Such roller switches may be operated by contact with a moving cam surface and are frequently used as position limit switches in various mechanical applications. In one such application, a passenger elevator, a roller switch is attached to the moving elevator car with the actuating cam surfaces fixed at the upper and lower ends of the elevator hoistway, whereby the roller switch is actuated as the elevator approaches the limits of travel defined by the hoistway. Alternatively, the locations of the roller switch and the actuating cam may be interchanged.
As such limit switches may be used to sense the presence of the elevator car in an area proximate to the ultimate mechanical limit of travel, it is critical that such switches, if they are not in proper operating condition, provide a signal or other failure mode whereby the system controls may detect the switch failure. In particular for roller switches, one failure mode would occur if the roller bearing or other roller attachment means were to detach from the switch arm. In this situation, the roller would fall or otherwise be lost from the roller switch, which would then, in the prior art, fail to contact the cam surface and thus fail to sense the presence of the elevator at or beyond its extreme motion limits.
What is needed is a roller switch which will signal the elevator control system in the event of a loss or detachment of the roller from the switch arm.